Telephone-exchange system



W. C. KIES E'L. I

TELEPHONE EXCHANGE'SYSTEM.

APPLICATION FILED FEB-1,1918- 1,330,474. Patented Feb. 10, 1920.

m 1 eh m5 Wa/fer 6 /f/@ 36/ rinrrnn sra rns earner oninon WALTER C. KIESEL, OF COLLEGE PARK, MARYLAND, ASSIGNOR '10 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent. Patented Feb. 10, 1920.

Application filed February 1, 1918. Serial No. 214,889.

To all whom it may concern Be it known that I, WALTER C. Krnsnn, a citizen of the United States, residing at College Park, in the county of Prince Georges and State of Maryland, have invented certain new and useful improvements in TelephoneEXchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems, and more particularly to such systems employing manual means for connecting an operators telephone set with the conne;ting circuit used for connecting telephone lines for conversation.

The object of this invention is to provide a system or this character in which secrecy of conversation is assured.

In accordance with this invention, it the listening key of a link circuit joining two subscribers lines is actuated when the receivers of the connected lines are oil the switchhooks, a source of tone supply is then connected with the receivers of the two connected telephone lines, whereby the subscribers know that the operator is listeningin and is also operatively associated with the operators receiver so that the operator may be advised that the link circuit, the listening key of which has been actuated, forms part of a talking circuit between two subscribers.

For a more complete understanding of this invention, reference should be had to the following description considered in connection with the accompanying drawing illustrating one embodiment thereof.

There are shown in the drawing two subscribers lines A and B which terminate at a central oflice at which is located a cord circuit C for interconnecting the lines. The apparatus, shown within the dotted rectangle X, is common to the cord circuits of an operators position, it being understood, of course, that, for convenience only, the two line circuits and the one cord circuit are shown, and that many such lines and a plurality of such cord circuits are, in practice, employed.

The subscriber A, in initiating a call, removes the receiver from the switchhook, causing the operation of line relay 5, whereupon line lamp 6 is lighted. The operator, observing the lighted condition of the line lamp 6, inserts answering plug {Z into line jack 8 of line A, whereupon the contacts of the jack 8 are opened, disconnecting the line relay from the line. The line relay is thereupon de'c'nergized and the line lamp extinguished. Answering supervisory relay 10 is operated upon the insertion of the plug 7 into the ack 8 and in operating prevents the lighting of answering supervisory lamp 11. The operator may thereupon actuate listening key 12 to connect the operators telephone set with the calling line. The actuation of listening key 12 closes a circuit including the left-hand winding of relay 13, contact 14: of listening key 12, alternate contact of supervisory relay 10, sleeve contacts of the plug 7 and the jack 8 and resistance 15 to ground. Relay i3 is marginal so that it does not close its contact when a circuit through only one of its windings is completed, but when both wind ings are included in circuit, its contact is closed for purposes which more fully hereinafter appear.

The operator, after being advised that connection is desired with the line of subscriber B, restores the listening key 12 to normal position and inserts calling plug 27 into line jack 28, thereby lighting calling supervisory lamp 29. Subscriber B is signaled by the actuation of a ringing key 30 which connects a source of ringing current 39 with the called-for line for operating the usual call bell 38. In response to the actuation of the call bell at station B, the receiver is removed from its switchhook,

thereby causing the energization of supervisory relay 31, which attracts its armature, opening the circuit of, and extinguishing the calling supervisory lamp 29.

E hile the receivers are oil the switchhooks and subscribers A and B are conversing, should the operator actuate listening key 12, the circuit, including the left-hand winding of relay 13, will be closed as before described and there will also be established a circuit for the right-hand winding of this relay 13, including contact 32 of listening key 12, alternate contact of supervisory relay 31, sleeve contacts of the plug 27 and the jack 28, and resistance 33 to ground. Since both windings of relay 13 are now traversed by current, the relay will attract its armature, closing a circuit which includes the contact and winding of a vibrating relay 3e and the tertiary winding of the 119 V on the conversation.

warns the subscribers whenever an operator operators induction coil 35. As long the contact of relay 13 is closed, relay 3% will be alternately energized and deenergized, opening and closing itscircuit which includes the tertiary winding of the induction coil'35. An alternating current will therefore be induoed into the secondary winding of this induction coil, thereby producing a tone in the receiver 36 and, since the secondary winding of the induction coil is bridged across the talking strands of the cord circuit C, this tone will also be produced in the receivers at stations A and B. The tone in the operators receiver 86 indicates to the operator that a talking connection exists between subscribers A and B and the tone in the subscribers receivers indicates to them that the operator is attempting to listen-in Therefore, this tone listening key when both supervisory relays are energized to operatively associate the source of tone supply with both. telephone 7 lines.

2. A telephone exchange system comprising two telephone lines, subscribers station apparatus, a link circuit connecting the lines together, an operators telephone set, a

listening key for connecting the operators telephone set with the link circuit, a source of tone supply, a relay for connecting the source of tone supply to the connected telephone lines, and an operating circuit for said relay jointly controlled by apparatus at the substations and the listening key.

switch.

3. A telephone exchange system comprising two subscribers telephone lines, a link circuit connecting the lines together, an operators telephone set, a listening switch for connecting the operators telephone set with the link circuit, a source of tone supply, a relay for operatively 'associatingthe source of tone supply with the receiver of the operators telephone set, and an operating circuit for said relay ointly controlled by ap paratus at the substations and the listening 4. A telephone exchange system compris ing two telephone lines, subscribers" substation apparatus including a receiver con nected with each line, a link circuit connecting the lines together, an operators tele phone set, a listening switch for connecting the operators telephone set with the link circuit, a source of tone supply, electromagnetic means to op'eratively associate the source of tone supply with the receivers of the two lines and with the receiver of the operators telephone set, and an operating circuit for said relay jointly controlled by apparatus at the substation and the listening switch.

5. A telephone exchange system comprising two telephone lines, subscribers station apparatus including a receiver connected with each line, a link circuit connecting the lines together, an operators telephone set, a listening key for connecting the operators telephone set with the link circuit, a source of tone supply, a relay responsive to the actuation of the listening key when the re-. ceivers of the two telephone lines are operatively connected therewith to connect the source of tone supply with the connected telephone lines, and means for preventing the operation of said relay in response to the operation of the listening key until the receivers of the two telephone lines are operatively connected.

In witness whereof, I hereunto subscribe my name this 19th day of January A. D.,

WALTER O. KIESEL. 

